There are many domestic and commercial applications wherein areas and surfaces must be protected against infestation by insects and other pests. For example, household cupboards, wardrobes, pantries and the like must be protected against invasion by ants, cockroaches and other pests. Similarly, in commercial premises and establishments such as restaurants, cafes and the like it is essential, and often mandatory under government health regulations, that areas used for the storage of food and/or the preparation and serving of meals be kept pest free.
Of particular concern are German cockroaches. These pests have a marked resistance to most of the known pesticides, including the synthetic pyrethroids. Conventional treatments only remove this species of cockroach for a period between several days and three months. Further, conventional treatments do not affect any eggs which may have been deposited by the female cockroach. Accordingly, the eggs hatch and re-infestation occurs.
In the past, organo phosphates were the preferred choice for the extermination and control of these pests, although they have been virtually superceded today by synthetic pyrethroids and carbamates. However, two well-known organo phosphates still in use are dichlorvos and chlorpyrifos. Dichlorvos is commonly used as a fumigant and thus used when it is necessary to kill pests already present in an affected area. Chlorpyrifos is a residual and is, therefore, utilised to keep an already cleared area free from pests. It is primarily used as a surface spray for short to medium-term residual control. Commercial suppliers of chlorpyrifos estimate its effective life to be approximately three (3) months. Nevertheless, individually, neither dichlorvos nor chlorpyrifos are considered to be very effective.
It is also known to provide a pesticidal composition which is a combination of fumigant and residual ingredients. In fact, dichlorvos has been used as an additive to a residual-type pesticide. Although when used as such an additive, dichlorvos does reduce the "knockdown" time required to eliminate existing pests, it does not increase the effective life of the residual ingredient to which it has been added. For this reason, dichlorvos is rarely used now in the pest control industry as the extra expense incurred in its inclusion in the composition to reduce the immediate numbers of pests present is not outweighed by any lasting advantage of the residual component.
Further, a disadvantage of the residual chlorpyrifos is that it is readily removed by cleaning of treated surfaces, such cleaning, of course, being a regular occurrence in food storage, preparation and serving areas.
Yet another disadvantage of prior pesticidal compositions, whether they contain residual ingredients or not, is that a pest usually must remain in a treated area for a sufficient period for the pesticidal composition to be effective. If the pest remains for that sufficient period, then often enough contact with the active ingredient has been made to eradicate the pest, even if the pest first leaves the treated area before dying. On the other hand, if the pest leaves the treated area before sufficient contact is made with the active ingredient, then the pest may again return to the area as it is unaware that that environment is hostile to it.